U.S. Pat. No. 5,233,853 discloses a device for simultaneously stretch straightening a plurality of side by side oriented segments of tubing for use in manufacturing heat exchangers and bending that tubing to form hairpin tubes. In the process of manufacturing a plurality of hairpin tubes simultaneously, difficulty was being encountered in keeping the legs of the "U" of the hairpin tubes to the same length. Varying frictional forces were occurring as each tube was being bent so that following a bending of a plurality of tubes, the length of the respective legs would be substantially different. During a lacing of the hairpin tubes into a stack of heat exchanger fins, the assembled hairpin tubes and heat exchanger fins would be presented to a work station whereat conventional return bends would be soldered to the open ends of the hairpins tubes to form a fluid circuit for the heat exchanger fluid (see U.S. Pat. No. 4,683,649). Automated soldering equipment require that the joint that is to be soldered be accurately presented to the robotics so that soldering can occur at a precise location. If the free open ends of the hairpin tubes are at differing heights, the return bends will not be properly located for other state of the art assembly operations. If a return bend is to be soldered in place, and the open ends are at differing heights, the return bends will not be properly soldered by the robotics by reason of the fact that the joint that is to be soldered is not present at the desired location.
Therefore, equipment which will accurately manufacture hairpin tubes wherein the lengths of the legs of the hairpin tubes are precisely controlled will be beneficial in the manufacture of heat exchanger coils.
Accordingly, it is an object of the invention to provide a tube bender method and apparatus which will accurately control the length of the legs of the U-shaped hairpin tube to a prescribed length.
It is a further object of the invention to provide a hairpin bender which will enable the bending of a plurality of such hairpin tubes simultaneously, each of the plurality of hairpin tubes having legs of a precisely controlled length.
It is a further object of the invention to provide the invention as an improvement to the tube bending structure illustrated in U.S. Pat. No. 5,233,853.